九江下蜀黄土的常量元素组成及其物源指示

Element Compositions of Xiashu Loess in Jiujiang and Its Implication for Provenance Tracing

长江中下游地区下蜀黄土的物质来源一直是个热点问题。对江西九江下蜀黄土和甘肃临洮晚更新世以来黄土的常量元素组成进行了研究,并与末次间冰期以来黄土高原其他点位的黄土、长江中下游其他地点的下蜀黄土和长江沉积物的元素组成进行对比,以期探讨九江下蜀黄土的物质来源。结果表明:1)九江下蜀黄土的地球化学组成以SiO_2、Al_2O_3、Fe_2O_3为主。与临洮黄土的元素组成相比,九江下蜀黄土具有较高的SiO_2、Al_2O_3、Fe_2O_3、TiO_2含量和较低的CaO、MgO含量;2)在空间上,下蜀黄土的SiO_2/Al_2O_3比值未表现出黄土高原黄土(北方黄土)的SiO_2/Al_2O_3比值随纬度规律性变化的特点,揭示下蜀黄土的主要源区可能不是北方的内陆荒漠或黄土高原;3)TiO_2/Al_2O_3-K_2O/Al_2O_3和TiO_2/Al_2O_3-Fe_2O_3/Al_2O_3图解显示下蜀黄土与北方黄土存在显著差异,进一步表明下蜀黄土与北方黄土的主要源区可能不同。

This study presents the major element compositions of Xiashu loess in Jiujiang,Jiangxi Province,and loess deposited since the late Pleistocene at Lintao,Gansu Province.The results are compared with element compositions of the other loess deposits deposited since the last interglacial on Chinese Loess Plateau,Xiashu loess at other sites and fluvial sediments in the middle and lower reaches of the Yangtze River.The aim of this work is to discuss the source area of the Xiashu loess in Jiujiang.The conclusions are drawn as follows:(1) Elements of Xiashu loess in Jiujiang are dominated by SiO2,Al2O3 and Fe2O3 oxides.Compared to major elements in loess at Lintao section,Xiashu loess in Jiujiang has higher contents of SiO2,Al2O3,Fe2O3,TiO2,and lower contents of CaO,MgO.(2) On the space,there is a significant rule in loess on Chinese Loess Plateau since the last interglacial:the higher latitude,the higher SiO2/Al2O3 values in sediments.However,this rule does not appear in the Xiashu loess in southern China,implicating that the Xiashu loess is probably not from the inland deserts in northern China or Chinese Loess Plateau.(3) Plots of TiO2/Al2O3 vs.K2O/Al2O3 and TiO2/Al2O3 vs.Fe2O3/Al2O3 show that obvious difference existed between Xiashu loess in southern China and loess in northern China.The result further indicates that the main source area of the Xiashu loess in southern China and loess deposits on the Chinese Loess Plateau is probably different.